Ceftibuten: Development of a Commercial Process Based on

development of several relatively low-cost orally active cephalosporins, for example .... lin sulfoxide esters, notably building on the rearrangement ...
0 downloads 0 Views 66KB Size
Download PDF
Organic Process Research & Development 2002, 6, 152−157

Ceftibuten:† Development of a Commercial Process Based on Cephalosporin C. Part I. Process for the Manufacture of 3-Acetoxymethyl-7(R)-glutaroylaminoceph-3-em-4-carboxylic Acid 1(S)-oxide Ermanno Bernasconi,‡ Junning Lee,§ Jacopo Roletto,‡ Loris Sogli,‡ and Derek Walker*,§ Chemical DeVelopment, Antibioticos, S.p.A., Via Schiapperelli 2, 10036 Settimo Torinese (TO) Italy, and Chemical DeVelopment, Schering-Plough Research Institute, 1011 Morris AVenue, Union, New Jersey 07083, U.S.A.

Abstract: The manufacture of low-cost, orally active cephalosporin drugs has, until now, been achieved using intermediates prepared by the ring expansion of penicillin sulfoxides rather than fermented cephalosporin C. This report describes the preparation of 3-acetoxymethyl-7(R)-glutaroylaminoceph-3-em-4-carboxylic acid 1(S)-oxide (8) from cephalosporin C broths. This new intermediate has been shown (see the following contributions) to be a superior starting material for the low-cost preparation of the orally active cephalosporin, Ceftibuten.

Introduction Most parenteral cephalosporin drugs are produced from 7(R)-aminocephalosporanic acid (7-ACA), itself derived from fermented cephalosporin C (4). Orally active cephalosporin drugs emerged from the vigorous programs of work to broadly exploit the superior properties of the cephalosporins in general, particularly their enhanced spectrum of activity, their greater stability to β-lactamases, and their improved safety profiles, versus the penicillins.1 Early on, efforts to understand the biological mechanism involved in cephalosporin formation led to the discovery2 of the ring-expansion of low-cost penicillin sulfoxides to 3-methylcephalosporins, a few of which were manipulated to create oral activity. The ring expansion discovery led to the identification and development of several relatively low-cost orally active cephalosporins, for example, cephalexin,3 cephradine,4 cefadroxil,5 and cefaclor.6 The continued search for orally active cephalosporins with broader biological spectrum led to new † Ceftibuten was discovered by Shionogi and Co. Ltd., Osaka, Japan, and licensed to Schering-Plough Corporation, Kenilworth, New Jersey. The drug is manufactured by Shionogi. ‡ Chemical Development, Antibioticos, S.p.A. § Chemical Development, Schering-Plough Research Institute. (1) Bucourt, R. In Recent AdVances in the Chemistry of β-Lactam Antibiotics; Gregory, G. I., Ed.; Special Publication No. 38; The Royal Society of Chemistry: London, 1981; p 1. (2) (a) Morin, R. B.; Jackson, B. G.; Mueller, R. A.; Lavagnino, E. R.; Scanlon, W. B; Andrews, S. L. J. Am. Chem. Soc. 1963, 85, 1896. (b) Morin, R. B.; Jackson, B. G.; Mueller, R. A.; Lavagnino, E. R.; Scanlon, W. B; Andrews, S. L. J. Am. Chem. Soc. 1969, 91, 1401. (c) Morin, R. B.; Jackson, B. G. (Eli Lilly). U.S. Patent 3,275,626, 1966. (3) Ryan, C. W.; Simon, R. L; Van Heyningen, E. M. J. Med. Chem. 1969, 12, 310. (4) Dolfini, J. E.; Applegate, H. E.; Bach, G.; Basch, H.; Bernstein, J.; Schwartz, J.; Weisenborn, F. L. J. Med. Chem. 1971, 14, 117. (5) Crast, L. B. Jr. (Bristol-Myers). U.S. Patent 3,489,752, 1970. (6) (a) Chauvette, R. R.; Pennington, P. A. J. Med. Chem. 1975, 18, 403. (b) Chauvette, R. R.; Pennington, P. A. J. Am. Chem. Soc. 1974, 96, 4986. (c) Chauvette, R. R. (Eli Lilly). U.S. Patent 3,925,372, 1975.

152 • Vol. 6, No. 2, 2002 / Organic Process Research & Development Published on Web 02/16/2002

compounds, most based on cephalosporin C, for example, cefroxadine,7 cefatrizine,8 cefixime,9 and cefprozil.10 The syntheses of these last four compounds were all inefficient, often requiring protection and deprotection steps, which added to their costs. Indeed the high cost of goods of the oral cephalosporin drugs derived from cephalosporin C significantly offset the attractiveness of their improved biological spectrum versus the above penicillin-based oral cephalosporins. The discovery of the parenteral cephalosporin ceftizoxime11 by Fujisawa Pharmaceutical Co. Ltd., and the oral cephalosporin Ceftibuten12 (1) by Shionogi and Co. Ltd., only exacerbated the cost-of-goods dilemma, since both of these cephalosporins are unique in carrying an H-substituent at the 3-position of the cephalosporin nucleus.

Introducing the 3-H substituent requires additional manipulations of the cephalosporin molecule for the conversion of the 3-acetoxymethyl group in cephalosporin C to 3-H. This has been achieved by converting acetoxymethyl to hydroxymethyl followed by oxidation of the hydroxymethyl group to the 3-aldehyde and finally decarbonylation and also by the Cr(II)-mediated reduction of the 3-acetoxymethyl (7) (a) Scartazzini, R; Bickel, H. HelV. Chim. Acta, 1974, 57, 1919. (b) Zak, O.; Vischer, W. A.; Schenk, C.; Tosch, W.; Zimmerman, W.; Regos, J.; Suter, E. R.; Kradolfer, F.; Gelzer, J. J. Antibiot. 1976, 29, 653. (c) Scartazzini, R.; Bickel, H. (Ciba-Geigy). U.S. Patent 4,073,902, 1978. (8) (a) Dunn, G. L.; Hoover, J. R. E.; Berges, D. A.; Taggart, J. J.; Davis L. D.; Dietz, E. M.; Jakas, D. R.; Yim, N.; Actor, P.; Uri, J. V.; Weisbach, J. A. J. Antibiot. 1976, 29, 65. (b) Dunn, G. L.; Hoover, J. R. E. (Smith, Kline and French). U.S. Patent 3,855, 213, 1974. (9) (a) Yamanaka, H.; Chiba, T.; Kawabata, K.; Takasugi, H.; Masugi, T.; Takaya, T. J. Antibiot. 1985, 38, 1738. (b) Takaya, T.; Hisashi, T.; Masugi, T.; Yamanaka, H.; Kawabata, K. (Fujisawa). U.S. Patent 4,409,214, 1983. (10) (a) Naito, T.; Hoshi, H.; Aburaki, S.; Abe, Y.; Okumura, J.; Tomatsu, K; Kawaguchi, H. J. Antibiot. 1987, 40, 991. (b) Hoshi, H.; Okumura, J.; Naito, T.; Abe, Y.; Aburaki, S. (Bristol-Myers). U.S. Patent 4,520,022, 1985. (11) (a) Takaya, T.; Takasugi, H.; Tsuji, K; Chiba, T. (Fujisawa). U.S. Patent 4,427,674, 1984. (b) Takaya, T.; Takasugi, H.; Chiba, T.; Tsuji, K. (Fujisawa). U.S. Patent 4,372,952, 1983. (12) (a) Hamashima, Y.; Kubota, T.; Minami, K.; Ishikura, K.; Konoike, T.; Yoshioka, M.; Yoshida, T.; Nakashimizu, H; Motokawa, K. J. Antibiot. 1987, 40, 1468. (b) Hamashima, Y. (Shionogi). U.S. Patent 4,634,697, 1987. 10.1021/op0100697 CCC: $22.00 © 2002 American Chemical Society

group to 3-exomethylene and thence, in a series of steps (ozonolysis to 3-hydroxycephem, reduction to 3-hydroxycepham, activation of 3-hydroxy and base treatment), to the 3-H cephem.13 From an economic standpoint, neither cephalosporin C-based route was attractive for commercial operation and led Fujisawa workers to develop a synthesis scheme based on the intermediates generated in Lilly work on cefaclor6 and Ciba-Geigy work on cefroxadine,7 in short returning to intermediates derived from penicillins.14 The added costs introduced by the molecular manipulations needed to access the 3-H compounds required for the parental drug ceftizoxime were held as justifiable since this compound offered biological advantages over the earlier parenteral cephalosporins. However, since the oral cephalosporins are generally administered at higher doses than their parenteral counterparts, what was economically acceptable for producing the parental Ceftizoxime molecule was unacceptable for producing the oral Ceftibuten molecule. Indeed the development of a practical, low-cost process for Ceftibuten posed severe challenges for the chemical development scientists and engineers in Shionogi. They evaluated cephalosporin routes to Ceftibuten15 but quickly decided not to pursue them in light of their earlier discovery and successful exploitation16 of a route to 3-hydroxycephems that was based on other starting materials derived from the rearrangement of penicillin sulfoxide esters, notably building on the rearrangement discovered by Cooper.17 The Shionogi route18 for converting penicillin G sulfoxide to Ceftibuten (Scheme 1) thus developed quite naturally from Shionogi’s position. The Cooper intermediate19 of choice is identified as compound 2 in Scheme 1. The step yields to diphenylmethyl 7(R)-aminoceph-3-em4-carboxylate 3, the key Ceftibuten intermediate, are good to excellent, and the quality of 3 is very high. However, not surprisingly, the large number of steps and intermediate isolations results in a high cost of 3, and hence a high cost of Ceftibuten. Although the use of a cephalosporin starting material, in place of the penicillin described in Scheme 1, would eliminate the several steps needed to convert the fivemembered ring in the penicillin to a six-membered ring, the high cost of cephalosporin C, and the additional steps needed to introduce the 3-H substituent, have until now proved an insurmountable obstacle to the use of this starting material for Ceftibuten manufacture. The main factor responsible for (13) (a) Peter, H; Bickel, H. HelV. Chim. Acta, 1974, 57, 2044. (b) (Ciba-Geigy). Br. Patent 1,356,437, 1974. (c) Peter, H; Bickel, H. (Ciba-Geigy). U.S. Patent 4,269,977, 1981. (d) Ochiai, M.; Aki, O.; Morimoto, A.; Okada, T; Shimadzu, H. J. Chem. Soc., Chem. Comm. 1972, 800. (e) Ochiai, M.; Aki, O.; Morimoto, A.; Okada, T.; Shinozaki, K; Asahi, Y. J. Chem. Soc., Perkin Trans. I 1974, 258. (f) See ref 7a, this paper. (14) Takaya, T.; Kochi, H; Masugi, T. (Fujisawa). U.S. Patent 4,246,405, 1981. (15) Yoshioka, M. Private communication. (16) Hamashima, Y.; Ishikura, K.; Ishitobi, H.; Itani, H.; Kubota, T.; Minami, K.; Murakami, M.; Nagata, W.; Narisada, M.; Nishitani, Y.; Okada, T.; Onoue, H.; Satoh, H.; Sendo, Y.; Tsuji, T; Yoshioka, M. In Recent AdVances in the Chemistry of β-Lactam Antibiotics; Elks, J. Ed.; Special Publication, No. 28; The Royal Society of Chemistry: London, 1977; p 243. (17) Cooper, R. D. G; Jose, F. L. J. Am. Chem. Soc. 1970, 92, 2575. (18) Yoshioka, M. Pure Appl. Chem. 1987, 59, 1041 and references therein. (19) Cooper’s original intermediate related to 2 carried a phenoxymethyl group in place of benzyl and the 2,2,2-trichloroethyl group in place of benzhydryl: ref 17, this paper.

Scheme 1. Synthesis of Ceftibuten nucleus

the high cost of cephalosporin C is the presence of the zwitterionic R-aminoadipoyl (R-Aad) side chain which introduces water solubility and with it the need for expensive recovery procedures to extract the molecule from fermenter broths. Many attempts have been made to overcome this problem. Glaxo workers20a,b described the enzyme-mediated conversion of the R-Aad side chain of cephalosporin C to the glutaroyl side chain, thereby introducing possibilities for solvent extraction, but did not reduce the process to practice. Asahi20c patented the same transformation using a ketone and hydrogen peroxide. Several groups21 have acylated the amino group of the aminoadipoyl side chain in fermentation broths to destroy the zwitterionic character, thereby allowing a solvent-extraction process (Bristol-Myers commercialised such a process21c,d). In a further variation of the derivatisation followed by solvent-extraction approach, Glaxo workers described extractive esterification of N-acylated cephalosporin C using diphenyldiazomethane22 and the formation and solvent extraction of a Hantzsch dihydropyridine derivative of cephalosporin C.23 The above derivatisation/extraction processes mostly depend on isolating the functionalised cephalosporin C product, purifying it, and then converting it to the key intermediate, 7-ACA, or an ester thereof, using conventional (20) (a) Arnold, B. H.; Fildes, R. A; Gilbert, D. A. (Glaxo). U.S. Patent 3,658,649, 1972. (b) Fildes, R. A.; Potts, J. R; Farthing, J. E. (Glaxo). U.S. Patent 3,801,458, 1974. (c) Suzuki, N.; Sowa, T; Murakami, M. (Asahi). U.S. Patent 4,079,180, 1978. (21) (a) Chauvette, R. R.; Hayes, H. B.; Huff, G. L; Pennington, P. A. J. Antibiot. 1972, 25, 248. (b) (Pfizer). Br. Patent 1,311,268, 1973. (c) Johnson, D. A.; Richardson, E. J.; Rombie, J. M; Silvestri, H. H.; Smith, R. R. (BristolMyers). U.S. Patent 3,573,296, 1971. (d) Brooks, T. J. (Bristol-Myers). U.S. Patent 3,830,809, 1974. (22) (a) Bywood, R.; Robinson, C.; Stables, H. C.; Walker, D; Wilson, E. M. In Recent AdVances in the Chemistry of β-Lactam Antibiotics; Elks, J. Ed.; Special Publication No. 28; The Royal Society of Chemistry: London, 1977; p 139. (b) Gallagher, G; Walker, D. (Glaxo). U.S. Patent 4,083,837, 1978. (c) Robinson, C; Walker, D. (Glaxo). U.S. Patent 4,059,573, 1977. (23) Stables, H. C.; Atherton, J; Matchan, M. J. (Glaxo). U.S. Patent 3,821,208, 1974. Vol. 6, No. 2, 2002 / Organic Process Research & Development

•

153

Scheme 2. Industrial process for 7-glutaroylcephalosporanic acid and 7-ACA production

chemistry, for example, PCl5 cleavage of the amide group of 7-ACA or an ester thereof.24 The several process steps needed in derivatization/extraction processes to 7-ACA involve organic solvents and require a great deal of process equipment. These operations add substantial labor, equipment depreciation, and chemical costs, which contribute significantly to the cost of 7-ACA produced via these routes. The efforts of others to find organisms which directly cleave the R-Aad side chain have met with little success, although Toyo Jozo workers25 did show that the enzymic cleavage of the glutaroyl side chain of products produced by Glaxo,20a,b to give 7-ACA, was feasible. Results and Discussion Recognizing the disadvantages and the costs associated with the above schemes to utilize cephalosporin C, Antibioticos26 reasoned that the use of immobilized enzymes, for both the enzyme-mediated conversion of the R-Aad side chain to glutaroyl and the enzyme-mediated cleavage of this side chain, should enable them to produce 7-ACA in an allwater system without isolating any intermediate or employing any solvent. This approach, outlined in Scheme 2, was validated and is now practiced commercially on a >100 tonne/annum scale. The process has been patented.27 (24) (a) Fechtig, B.; Vischer, E.; Bickel, H.; Bosshardt, R.; Bosshardt-Schar, R. E; Urech, J. U.S. Patent, 3,875,151, 1975. (b) Fechtig, B.; Peter, H.; Bickel, H; Vischer, E. HelV. Chim. Acta, 1968, 51, 1108. (25) Matsuda, T.; Yamaguchi, T.; Fujii, T.; Matsumoto, K.; Morishita, M.; Fukushima, M; Shibuya, Y. (Toyo Jozo Kabushiki Kaisha). U.S. Patent 3,960,662, 1976. (26) Cabri, W.; Verga, R.; Cambiaghi, S; Bernasconi, E. Chim. Ind. 1999, 81, 461. (27) Cambiaghi, S.; Tomaselli, S; Verga, R. (Antibioticos, S.p.A.). U.S. Patent 5,424,196, 1995. 154

•

Vol. 6, No. 2, 2002 / Organic Process Research & Development

The efficiency of the approach described in Scheme 2 is apparent from further detail of the handling of the process. The principal product of the fermentation of Cephalosporium acremonium is cephalosporin C (4), generally mixed with small amounts of desacetyl (5) and 3-methyl (6) compounds. The thick fermentation broth is ultrafiltered to remove the mycelium and high-molecular-weight substances. The clear solution is purified through an adsorption-elution process on macroreticular resins.28 The purification step is needed to reduce the amounts of 5 and 6 and to eliminate proteinaceous and carbohydrate materials in the fermentation broth. The purified solution, decolorized with ion-exchange resin,29 and containing mostly cephalosporin C, is then enzymatically converted into 3-acetoxymethyl-7(R)-glutaroylaminoceph-3-em-4-carboxylic acid (7) using an immobilized D-amino acid oxidase [DAO] derived from a Rhodotorula microorganism, particularly R. gracilis (ATCC 26217). The reaction rate is monitored by HPLC. The oxidation reaction is generally rapid (1-2 h); however, to enhance production rates, shorter times are employed, and the residual intermediate, 3-acetoxymethyl-7(R)-(5′-ketoadipoyl)aminoceph-3-em4-carboxylic acid, oxidized to 7 using a small excess of hydrogen peroxide. The solution of 7 obtained from the above process is then submitted to a second enzymatic step to obtain 7-ACA using immobilized 7-glutaroyl ACA acylase [GLA]. The immobilized enzymes are recycled many times. Both the (28) XAD 16 (Rohm & Haas); HP 20 and SP 825 (Mitsubishi Chemical Corporation). (29) IRA 68 (Rohm & Haas); WA 20 and WA 30 (Mitsubishi Chemical Corporation).

enzymes are produced by fermentation of highly selected recombinant producer strains, extracted, purified, and immobilized. 7-ACA is precipitated by adjusting the pH of the solution to 3.5-4.0, filtered, washed, and dried. The quality of purified 7-ACA obtained from the enzyme-mediated process is equivalent (containing 2.0] was adjusted to pH 2.3 with 40% H2SO4. The solution was applied (at flow rate of 1.5 bed vols (BV)/h) on 14 L of adsorbent resin (XAD 16) charged into a column (height 100 cm; diameter 15 cm). The resin was previously adjusted to pH 2.3 with 10% H2SO4. Water (14 L) was then passed through the column (flow rate 1.5 BV/h). The elution of cephalosporin C was monitored by HPLC. The yield in the purification step was >95%. The purity of the solution of cephalosporin C was 85-90% (area % HPLC), A420nm ) 0.6-0.8. 156

•

Vol. 6, No. 2, 2002 / Organic Process Research & Development

Purified solution (42 L) was decolorized with 2.8 L of ion-exchange resin (IRA 68) at pH 6.0. The resin was charged into a column of height 150 cm and diameter 2 cm. The flow rate of the decolorization was 2.5 BV/h. The yield in the decolorisation step was >95%. Decolorized solution (42 L) containing 239.0 g of cephalosporin C (A420nm < 0.1) was evaporated to reach a volume of ca. 10 L and then fed into a 20-L reactor with 840 g of immobilized wet D-amino acid oxidase. Incubation was conducted at 25 °C under slight stirring and with an oxygen flow through a bottom diffuser of 1 vol/vol/min. The pH was maintained at 7.5 by automatic additions of 5% ammonia. In 75 min the cephalosporin C was completely transformed. The percentage composition of the cephalosporin C transformation products was 3-acetoxymethyl-7(R)glutaroylaminoceph-3-em-4-carboxylic acid (88%), 3-acetoxymethyl-7(R)-(5′-ketoadipoyl)aminoceph-3-em-4-carboxylic acid (6%), and other (4%). The solution obtained after incubation was separated from the immobilized enzyme mass by filtration. For each liter of filtrate 56 mL of 3.5% hydrogen peroxide was added under stirring. The mixture was left for 15 min at 25 °C after which 2.8 g of sodium pyruvate was added. The purity of the solution of 3-acetoxymethyl-7(R)-glutaroylaminoceph-3-em-4-carboxylic acid 7 was 93% (area % HPLC). A sample was taken and crystallised to give a solid product for characterisation. This was done by diluting the solution obtained after the sodium pyruvate treatment with deionised water to a concentration of 7 of ca. 20-25 g/L. Sodium chloride (1.5 kg) was added to a 10 L quantity of the solution of 7 and the mixture stirred until all the NaCl had dissolved. The pH was adjusted to 1.5 to 2 using 18% hydrochloric acid. The crystals of 7 were filtered and suspended in water (1.5 L), stirred for 30 min, filtered, and dried. 1H NMR (400 MHz, DMSO-d6): δ 1.72 (m, 2H), 2.03 (s, 3H), 2.21 (m, 4H), 3.48 (d, 1H, J ) 18 Hz), 3.62 (d, 1H, J ) 18 Hz), 4.68 (d, 1H, J ) 12.8 Hz), 4.99 (d, 1H, J ) 12.8 Hz), 5.08 (d, 1H, J ) 4.8 Hz), 5.67 (dd, 1H, J ) 8, 4.8 Hz), 8.85 (d, 1H, J ) 8 Hz), 12.75 (bs, 2H); 13C NMR (100 MHz, DMSO-d6): δ 174.9, 173.5, 171.1, 165.6, 163.7, 127.4, 124.0, 63.6, 59.9, 58.3, 34.7, 33.7, 26.4, 21.4; FAB HRMS calcd for C15H19N2O8S (MH+) m/z 387.0862 found 387.0850. Oxidation of 7 to 8 in Aqueous Na2CO3 Solution. 7 (200 g, 93% purity, 0.48 mol), isolated as above, was suspended in 1.2 L of water and was added to a three-neck round-bottom flask equipped with agitator, thermometer, and addition funnel. The slurry was cooled to 0-5 °C. A solution of Na2CO3 (54.8 g, 0.518 mol) in 800 mL of water was added slowly. The mixture was agitated at 0-5 °C until dissolution was complete. Peracetic acid (32%, 100 mL, 0.48 mol) was added over 30 min while the reaction temperature was maintained at 0-5 °C. The oxidation was monitored by HPLC. After the reaction was complete, a sample was taken for lyophilisation and NMR analysis. The solution of the reaction (>95% solution yield) was used for further chemical transformations (comparative Zn/H+ reductions; see Part III30b) without isolation. A sample was prepared for analysis using the method described in the previous experiment. 1H

NMR (400 MHz, DMSO-d6): δ 1.73 (m, 2H), 2.02 (s, 3H), 2.29 (m, 4H), 3.57 (d, 2H, J ) 18.4 Hz), 3.82 (d, 2H, J ) 18.4 Hz), 4.60 (d, 1H, J ) 12.8 Hz), 4.86 (d, 1H, J ) 3.8 Hz), 5.21 (d, 1H, J ) 12.8 Hz), 5.76 (dd, 1H, J ) 8, 4.8 Hz), 8.19 (d, 1H, J ) 8.5 Hz); 13C NMR (100 MHz, DMSOd6): δ 176.0, 174.6, 172.1, 165.8, 164.2, 122.7, 110.1, 67.4, 64.7, 59.3, 46.5, 34.9, 34.0, 21.7, 21.6; FAB HRMS calcd for C15H19N2O9S (MH+) m/z 403.0811; found 403.0801. Pilot-Scale Preparation and Isolation of 3-Acetoxymethyl-7(R)-glutaroylaminoceph-3-em-4-carboxylic Acid 1(S)-Oxide (8). 3-Acetoxymethyl-7(R)-glutaroylaminoceph3-em-4-carboxylic acid (7) wet crystals, prepared as above, (titer HPLC: 45.4%; HPLC purity: 96.1%; Water K.F.: 45.6%; 37 kg as dry product) were suspended in 925 L of anhydrous isopropyl alcohol. The suspension was stirred and

cooled to a temperature of 2-4 °C. Peracetic acid (40% corresponding to a 40-45% of molar excess (referred to 3-acetoxymethyl-7(R)-glutaroylaminoceph-3-em-4-carboxylic acid) was added over 180 min. The suspension was stirred for 12 h at a temperature of 2-4 °C. The suspension was then filtered on a filter screen and the filter cake was washed with 370 L (0.4 vols referred to the volume of the solvent used for the reaction) of anhydrous isopropyl alcohol. The white crystals were dried in a vacuum oven, at a temperature of 28-32 °C, for 36 h. The total yield of 3-acetoxymethyl7(R)-glutaroylaminoceph-3-em-4-carboxylic acid 1(S)-oxide (8) was 36.5 kg (95%), purity, 98% (area % HPLC). Received for review August 21, 2001. OP0100697

Vol. 6, No. 2, 2002 / Organic Process Research & Development

•

157